My buddies firebird has a pretty severe water leak directly below the glove box inside the car. It only happens when the AC is on. We think it has something to do with the AC drainage hose being blocked since there is no leakage under the car like normal. Does anyone know where we can find the hose or have any other suggestions.

 

Make sure the A/C drainage hose is even still on there. I haven't looked at my Firebird so I'm not 100% positive, but on other late model GM cars I've worked on, there is a tray with a spout on it that forms the bottom of the AC/heater box. Water drips off of the evaporator down into the tray. The spout goes through the firewall where it connects to a rubber 90° boot hose to route the water outside. That hose is just a slip fit and over time can come loose. If it does, water won't go all the way out of the cabin. It will come out of the spout, hit the firewall and leak into the floorboard of the car. Check to make sure that panel isn't cracked where it can leak and that the hose is fully seated and not cracked.

 

I had that on my Z28. There is a drain hole on the bottom of the heater box that clogs up. Get a long screwdriver or unfold like a coathanger or something, and press it up there, you'll get a crapload of water coming out, and it'll be fine. It's hard to see it unless the car is up in the air, though.

What's happening is that the condensation is building up in the heater box, and with a plugged drain, it has noplace to go, so it spills over into the interior.